Intermittent Fasting & Fertility

Does Intermittent Fasting Negatively Affect Fertility In Women?

This is one of the most common questions I have been asked by women who are intermittent fasting, or interested in intermittent fasting.

The biology that underlies human female fertility is so complex that it is somewhat surprising that humans have continued to successfully reproduce for millennia. Ovulation, implantation, and early fetal development require a careful orchestration of several hormones including luteinizing hormone (LH), follicle-stimulating hormone (FSH), estrogen, and progesterone. If these hormones are too high or too low at a specific point in a woman’s cycle, conception will simply not take place. Therefore, women who are attempting to become pregnant are right to be curious about the effect of intermittent fasting on fertility.

Humans, like all mammals, are quite good at adapting to their environments. However, adequate nutrition may not always be available. When food is not plentiful, it is more taxing on the mother to create new life and then provide for them once they are born. Consequently, a mammal tends to respond to the relative abundance or scarcity of food by changing its internal fertility.

Consider an extreme example, namely infertility in women who suffer from anorexia nervosa. Women with the mental illness anorexia severely restrict their caloric intake, exercise aggressively, and obsess about food and body weight. Consequently, women with this disorder tend to become dangerously underweight. One of the other consequences of anorexia nervosa is amenorrhea, which is the medical term for a cessation of menstrual periods.1 The rapid and sustained weight loss coupled with rigorous exercise affects the hypothalamus and pituitary gland. It disrupts those important hormones, LH and FSH.2,3 In essence, self-starvation and weight loss below healthy levels causes infertility.

Of course, anorexia nervosa is an extreme example. Unfortunately, very few clinical studies have directly looked at the effects of intermittent fasting on fertility in women.4 Most are focused on periods of famine, starvation, or diseases—all of which bear little resemblance to intermittent fasting. Nevertheless, these studies do show, on some level, that fasting and reproduction are linked.

Let’s look at what we do know (unfortunately, it is mostly gleaned from experiments in rodents, not humans). Moderate calorie restriction can extend female reproductive capacity later into life (in adult mice).4 In other words, mice that were only allowed to feed for certain periods of time were able to produce offspring later than they would be if they were fed ad-libitum (fed freely).3,5 This may be due to the fact that eggs contained within ovaries (in mice) do not degenerate as quickly in those under calorie restricted diets.5

Is there any information about intermittent fasting on fertility in women (humans!)? Sadly, aside from extreme fasting and starvation, there is very little. Dutch women who experienced famine during World War II (about 500 calories per day for 6 months) were more likely to have irregular menstrual cycles, but did not have any perceptible decrease in fertility or ultimate family size.6 In fact, fetuses during this famine eventually had more children, more twins, and were less likely to be childless when they became adults.6 On the other hand, women who experienced this World War II famine entered natural menopause three months earlier on average than those who did not, which is the opposite of what occurs in mice.7

So, does intermittent fasting negatively affect fertility in women? While it may sound like a Magic 8-ball response, the answer is unclear at this time. Drs. Skaznik-Wikiel and Polotsky recently reviewed the pros and cons of continuous or intermittent calorie restriction on reproductive health and determined that, well, we simply do not know the answer.4 While the authors state “intermittent fasting may be beneficial for overall health and well-being” they also state the “potential detrimental impact of intermittent fasting on reproduction…ought to be studied.”4 They go on to warn women that too little is known about intermittent fasting and fertility in humans to know whether it positively or negatively affects fertility or has any effect whatsoever.

Case Study:

"I started Modified Alternate-Day Fasting (ADF) April 1, 2013 and successfully lost 20 pounds in three months. Once in maintenance mode, I continued Modified ADF, but only did two low calorie days per week and increased my calories on my other days. Every once in a while during maintenance mode, I temporarily switched to 16/8 or 20/4, or did a combination simply to break up the monotony.

In October of 2014 my husband and I decided to start a family. Since I was 36 years old, and was on birth control pills for 20 consecutive years, I decided I wanted to do everything I could nutritionally to increase my chances of conceiving naturally. After discontinuing birth control, my doctor recommended waiting three months before we started trying to make sure everything was functioning properly on its own. During those three months, I switched to 16/8 maintenance calories and increased my fats to 30% (previously I had them set at 25%). I read a study involving non-fat dairy and how it affects fertility so I switched out my low-fat or non-fat dairy with whole milk (for use in my shakes) and 2% Greek yogurt instead of non-fat Greek. I continued to limit my processed food intake and made sure to take my prenatal vitamins daily. On the first month we tried, I became pregnant! I believe your diet plays a big part in fertility. Ovulation is definitely affected if you are not eating enough and if you are under any stress at all. In my experience, I do not believe my 1 & 1/2 years of modified alternate-day fasting affected my fertility at all."

~Sara Young

Start Fasting Today:

Are you tired of following a calorie-restricted meal plan and exercising for hours to get results you can never maintain? Has your body stopped responding to diet & exercise??

Contrary to popular belief, there is a way to lose fat while building muscle, and it's called Intermittent Fasting (IF). And because it's effortless, you can maintain your results.

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Dr. Sara Solomon is the creator of the Fat Loss Fast System about Intermittent Fasting and Flexible Dieting. She has degrees from McGill University in dentistry (DMD) and physical therapy (B.Sc. PT). She is also a certified StrongFit Coach, CrossFit Level 1 Trainer, ACE personal trainer, NASM fitness nutrition specialist, Mad Dogg Spinning Instructor, Level 2 Buddy Lee Jump Rope Trainer and Ambassador, a Team Bodybuilding.com and BSN athlete, and a retired PRO Fitness Model. Her passion is teaching others how to fuel and move well.

4 Comments

Frine Santiago
July 10, 2015, 12:37 pm

This is my experience with fasting and fertility. I have been diagnosed with “unexplained fertility” since around 2011. My husband and I have been trying to conceive for about 5-6 years. In an attempt to clean out my system and hopefully help with fertility I started eating raw vegan. I ate raw vegan for about 3 months. My energy was through the roof but I immediately lost my period. I did not have a period the entire time I was eating raw vegan. I thought you had to be underweight for that to happen, but I still had the same belly pooch and I was 20 lbs over. I did consume however enough calories. I had to buy a larger fridge and my counters where full with produce. In retrospect, my fats and proteins were drastically reduced to almost<5%. It was hard for me to consume enough nuts to increase my fat content and we already know that plants have protein, however I would have to consume very unrealistic large amounts of that too. Aside from losing my period, my estrogen shot through the roof and I did not lose one single pound. I was not exercising during this period either.

Fast forward 6 months, and I came across fasting. I was really scared it would disrupt my cycle but I had to try it. I started with 20/4 and allocated my macronutrients to ensure I had at least 20-30% fat and protein. I did this for 2 months as my "test phase". I keep my exercise to less than one hour. I can happily say IF did not affect my cycle. My husband and I have not been trying to conceive for the past year, therefore I do not have a testimonial about that but I can say that IF has not affected my cycle or reproductive hormonal levels in a negative way. I continue to adapt the different IF methods depending on my life routine without negative effects to my cycle. Hope this helps.

Dr. S,
I’m so glad you wrote this article! I seem to be discovering articles at an increasing rate regarding the “dangers” of intermittent fasting for women.

For some reason, however, I get the sense that these women who are alleging that intermittent fasting has been dangerous from them, have also combined weight loss and fitness protocols that really messed with their system.

I’ve been practicing capital I capital Avenue for about five weeks now, and started with your six-day kickstart. It’s been amazing for me! I’ve lost 6.5 pounds in four weeks.

I have increased energy, my normally sluggish bowels have picked up significantly, and I much more intentional about what I eat and when I eat it, which for my eating personality is a great thing.

As you continue your research and expertise in this area, I’d love to see your thoughts on the general hormonal impact for women, as that’s another thing I’ve seen pointed to as a big danger.

I’d also love to see you talk about your approach to hiit training, as most trainers suggest not doing hiit more than three times a week, but your programs appear to suggest you do it six. I’m wondering if that presents long-term problems for your body?

Messing with my reproductive health is still my main concern for IF to he honest. On the other hand though, ANY weight loss program can have that effect when done to an extreme.
I was eating mainly raw vegan with a cooked dinner for over a year my period was as regular and normal as before despite very low fat and protein. (just to give a counter experience the poster above)
Being super stressed out during a level exams caused no problems either.
The reason why i am so worried about this is because i had anorexia some years ago and lost my period from day one of being so very restricive. And i know it can happen to people who are not underweight at well.
And i´m so scared of that happening again now that i have some weight to lose.
I just hope that observing my emotional and physical well-being carefully and modifying my intake and exercise routine if needed will be sufficient to ensure a regular cycle.